A 63 kg boy and sled are pulled along level ground with a force of 577 N. The boy and sled are moving at a constant velocity of 2.4 m/s. What is the size of the frictional force?

Tornadoes form in unusually violent thunderstorms when there is sufficient (1) instability and (2) wind shear present in the lower atmosphere. elaborate on what does instability mean when discussing the formation of a tornado? a) dry air in the middle atmosphere being rapidly cooled by rain b) winds at all levels of the atmosphere are strong and turn with height c) an isolated strong thunderstorm just ahead of a squall line that merges with the squall line d) very warm, humid conditions in the lower atmosphere; cooler than usual conditions in the upper atmosphere